Polybutylene terephthalate resins have excellent mechanical characteristics, electrical characteristics, heat resistance, weather resistance, water resistance, chemical resistance, and solvent resistance and are therefore widely used as engineering plastics in various uses, such as automobile parts and electric and electronic parts.
However, the polybutylene terephthalate resins have a problem of low hydrolysis resistance and do not necessarily have sufficient durability to be used in high temperature and high humidity environment.
Accordingly, improvement in the hydrolysis resistance of a polybutylene terephthalate resin composition has been investigated from the aspect of raw materials. For example, Patent Document 1 discloses a polybutylene terephthalate resin composition comprising a polybutylene terephthalate resin, a carbodiimide compound, and a fibrous filler. According to Patent Document 1, the resin composition described in Patent Document 1 has high strength and excellent heat shock resistance and also shows high tensile strength retention (hydrolysis resistance) after a pressure cooker test. However, the resin composition described in Patent Document 1 has a problem of an increase in viscosity due to a reaction between the polybutylene terephthalate resin and the carbodiimide compound. In addition, according to examples of Patent Document 1, the addition of a fatty acid ester to the composition can slightly increase the fluidity, but deteriorates the hydrolysis resistance.
It is also known that the fluidity of a resin composition during molding can be improved by adding a fluidity-improving agent to a polybutylene terephthalate resin. For example, Patent Document 2 discloses a polybutylene terephthalate resin composition having excellent fluidity by containing a glycerin fatty acid ester therein. In this Document, no technology of improving hydrolysis resistance has been found.
Patent Document 1: PCT International Application, Publication No. 2009/150830
Patent Document 2: PCT International Application, Publication No. 2009/050859